Junction transistor oscillator circuit



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April 17, 1956 e. B. HERZOG 2,742,571

JUNCTION TRANSISTOR OSCILLATOR CIRCUIT Filed Dec. 31, 1953 INVENTOR.

JTTORNEY v 2,142,571 JUNCTION TRANSISTQR oscrnrnron Gerald B. Herzog, Princeton, J., assignorLto Radio Corporation of America, a' corporation .or Delaware i er afi e D e h r 1 11 materna s me 11 "Claims. {6!(250-36) This invention relates 'to electrical signal generators or oscillator'cireuit-s and in particular to such circuits utilizing semi-conductor devicesofthe junction'type.

' The recentdevelopmentof-cornmercially useful semiconductor devices of the type employing a semi-conductive element having three contacting electrodes has already h ad ad'ecided eifect upon, and has caused the-introduction of many new techniques in the electric signal communication "field. These de'vicesfkriown extensively as transisters, are small in size especially'when compared with the ordinary vacuum tube, require no heater poweig are m durable and consistofmaterials -which" appear to have a long usefullifei Therefore, the use of transistors for oscillator as well as'other circuit applications hasbeen contact rtype. Point-contact transistors, as is well ;l nown 'zinthea'rt, may :becurrent.m tltiplieationflfiv' sand an y .pnder certain conditions, vexhibit .a negative resistance.

EEhus, oscillator hav ibp- (d signed sin ,peintz enta itransis m whi do n t enu r an xt tne .tf edbeek oat ,Her te etejhewever i a ih enra el y .ee e de n s a t ;p ov de an. externa ee hee etl sustain oscillations in those circuits utilizing junction transiste s- 4 lseeen tdevelepmente av nd eated-tha iun tien t ensist r s nete l e bee-re e 'ane' eem- .mum e l s ems .et .al rees- Ihu some up ;h emdy e rece ing sv tett l h relie e let nl fyiesjand s gnal detect on-s a es ma all use (j n tion tyn n sttb .eB eus o t e mpl ciiyje ,newn .pei t-eeatee tra sisto Qseil ate ire'uits, howeve th l eee er may .e l e .ese llate circui s o th latte t pei e junction transistors themselves recommends themforra- :dio frequency circuit applications. It has been found; forexample thatt due to' the'stability of the characteristics of junction transistors, their performance may be pr ediet'ed-with relative accuracy in ,various circuit applicavteus, of c u se t a th exe use of ne pe e provide an improved and simplified oscillator circuit which utilizes a semi-conductor .device having a current gain less than unity. I i I It is a further object of the present invention to provide an improved low cost electrical signal generatoricitcuit utilizing a junction transistorasthe signal amplifying element. i i f It is still another object of the present invention to -pro:' videa semi-conductoroscillator circuit .u-tiliz'in'g. a transistor of the junction type wherein external feedback means-may beeliminated. i r T It'is yet another object of the present invention to .provide an improved oscillator circuit whichutilizes a negative resistance characteristic of a junction-transistor'lto establish and maintain stabilized oscillations. '1

These and further objects and advantages of the present invention are achieved by the discovery, :in accordance .with the invention, that junction transistors may exhibit a negative resistance characteristic over a port-ion of their operating region it properly biased. This negative resistance characteristic of the junction transistor is used in accordance with the invention to sustain oscillations a parallel resonant tuned circuit. Th us, a'junction t'ran sistor oscillator is possible without the provision of external-feedback. i I i The novel features that are consideredcharacteristic of this invention are'set forth withparticularity in the appended claims. The inventionitself, however, both as to its organization and method of operation, as Well as additioiial objects and advantages therofg'will best beu'ndeirs'tood from the following description when read connection with thefaccomp'a' nyin'g' drawing, ;in which: T Figure 1 is a'scheinatic'lcircuit' diagram of a'transistor oscillator circuit utilizing a P---N-P junction transistorconnected in accordance with the present invention;

Figure 2 is a graph showing a curve relating collector current to collector voltage of atransistor of the type-illustratedinFigure 1; and i Figure '3' is a schematiccircuit diagram of the radiofrequency section of a signal receiver'embodying'the oscillator ofFigure lip accordance withthe invention.

Referring now to the drawing, whereindike elements are designated by like reference numerals throughout the jigures, and referring particularly to 'Figure l, a =junction transistor 8 of the-P NP type includes a semi-conductive .b ody ltl and three contacting electrodes which have'been e si a et a an em te lgfe e et r a a 1 To provide proper biasing potentials for oscillator operati oh,,in accordance with the invention, thengative terrnh nal of a battery 18 is connected directly with'the' base lfi e app n e fi ed bi Y l es here e- T e' Pa I terminal of the battery 18 is returned to a source'of ed reference potential or ground for thesystemas sh n. -While a P-N-P transistor ;has been used tolillusl ihte the invention, N-P-N junction transistors may be used by reversing.the polarity.of thebiasing source. 3 i

To provide a variable or adjustable biasing voltage source .for the collector 14,21 hatteryzfi h as itsneg'ative t mina een ete hr h e t nfie em voltage divi ie t eiste gl ens an ad ustabl epfi Th ta 24 is nn tejdte e e ii e enfind e flfi wh in combination with a capacitor 28 forms a parallel teeene 'e tenab e a e reu 3 ,.fe th 1 ei m "T e e paeit I i variable; e tun n the nk .eitelli 13. 19

any es e und m n a f qu n heliis veltea .end of the inductor 26 is connecteddirectly to the collector 14 of the transistor ,8. To complete the oscillatorcirw he e t 1.2 o ransis i eni eete t9 t 're f f fixed ef re po ent o zg oundte he tern. V V Ais slrown,.the'transistpr 8 is'biased for normal amplifier a t-9 t e em Fe base 16 while the collector 14 is negative with respect to the base 16. Thus, the collector 14 is referred to as being biased in the relatively non-conducting or reverse direction with respect to the base, While the emitter is referred to as being biased in the relatively conducting or forward direction with respect to the base.

It has been found, in accordance with the present invention, that a high percentage of junction transistors will exhibit a negative resistance characteristic if a fixed bias is applied to their base. This is accomplished if the transistor is connected as shown in Figure l of the drawing.

A typical collector electrode characteristic curve for a P-N-P transistor utilized in an oscillator circuit in accordance with the invention is shown in Figure 2. As the collector voltage increases from zero the collector curent also increases. So long as increases of the collector voltage yield an increase in the collector current, the so-called incremental resistance is positive. At point A, however, the characteristic of the transistor changes. For a typical P-N-P unit, the collector voltage with respect to the emitter is approximately 0.3 volt at this point. After reaching point A, the collector current begins to decrease, even though the collector voltage continues to rise. Thus, in the operating range between point A and point B, which is about 0.5 volt for the typical transistor, an increase in voltage will result in a decrease in collector current. Accordingly, the transistor exhibits negative resistance over this operating range. This negative resistance, which is voltage controlled, has been found to be most pronounced for collector currents exceeding twenty milliamperes and is increased with increasing collector currents.

The negative resistance characteristic exhibited by transistor 8 is used in accordance with the invention to supply the losses of the tuned circuit 30 and sustain oscillations therein. Hence, a junction transistor oscillator connected as described above is possible without the conventional external feedback paths. Oscillations may be taken from any convenient point in the circuit, as from a lead connected with the high voltage end of the tuned circuit 30, or as shown and described in connection with Figure 3.

The oscillator circuit which comprises the present invention may find wide application in electronic communication circuits of all types. Thus, it may find application as a source of fixed frequency oscillations. It is also apparent that this type of oscillator circuit may be used as the local oscillator in a superheterodyne receiver.

Thus, for example, in Figure 3 the oscillator signals appearing in the inductor 26 of the oscillator tank circuit 30 may be inductively coupled through the output coil 32, and serially therefrom through a coupling winding 34 I of a loop antenna 36 to the anode of a crystal diode 38 acting as the mixer or first detector of the receiver. One terminal of the coupling or output coil 32 is grounded as indicated.

The oscillator circuit may further be identical with that of Figure l and is so shown in Figure 3. Therefore, the frequency of the oscillatory energy may be varied by the capacitor 28 in the tank circuit 30.

The loop antenna 36;may comprise a ferromagnetic core or rod 40 which has signal pickup winding 42 mounted thereon in inductively coupled relation to the coupling winding 34. The antenna winding 42 is tuned for response to incoming signals by a variable capacitor 44 connected in shunt relation thereto as shown.

The cathode of the heterodyne crystal mixer 38 is connected to a low impedance matching tap on a tuning inductor 46 of a frequency selective or resonant intermediate frequency output circuit 48. To form a parallel resonant circuit which is resonant at the selected intermediate or beat frequency, the inductor 46 is shunted by a tuning capacitor 50. The output or intermediate frequency signal may be obtained from suitable terminals 52 of an intermediate frequency output inductor 54 inductively coupled to the inductor 46 as shown.

.Incoming signals induced in the loop antenna 36 are applied through the winding 42 to the crystal mixer 40 where they are heterodyned with local oscillator signals from the coil 32, to produce heat or intermediate frequency signals which may here be assumed to have a frequency corresponding to both the sum or difference of the signal frequency and the oscillator frequency. The resonant circuit 48 may therefore be tuned to the difference frequency, and conveys the intermediate frequency resultant signal to the output terminals 52 for further amplification as is well known.

As described herein, an improved oscillator circuit in accordance with the invention employs a junction transistor which does not require the provision of an external feedback path. The invention provides a relatively stable circuit which utilizes a minimum of circuit elements, thus achieving simplicity with reliability.

What is claimed is:

1. An oscillator comprising a semi-conductor device having a semi-conductive body, a base electrode, a collector electrode and an emitter electrode in contact therewith, said device being characterized by a current gain of less than unity, means including a source of operating bias voltage for applying a fixed voltage to said base electrode wherein said device exhibits a negative resistance characteristic over a portion of its operating range, and means providing a frequency determining circuit for said oscillator connected with said collector electrode and tunable for response to an alternating current of predetermined frequency,

2. An oscillator as defined in claim 1, wherein said frequency determining circuit means provides a parallel resonant circuit comprising a tuning inductor and shunt tuning capacity means therefor.

3. An oscilator as defined in claim 2 wherein said semiconductive body is of the PN-P junction type.

4. An oscillator as defined in claim 2 wherein said semiconductive body is of the N-P-N junction type.

5. In an oscillator circuit, the combination with a semiconductor device of the junction type having a semi-conductive body, a base electrode, a collector electrode and an emitter electrode in contact therewith, of means for applying an operating bias voltage between said base electrode and said emitter electrode in a relatively conducting polarity and for applying an operating bias voltage between said base electrode and said collector electrode in a relatively non-conducting polarity, said base bias being fixed wherein said device exhibits a negative resistance characteristic over a portion of its operating range, and a frequency determining circuit connected with said collector electrode and responsive to alternating currents of a predetermined frequency.

6. In a radio receiver, a tunable local oscillator comprising a semi-conductor device having a semi-conductive body, a base electrode, a collector electrode and an emitter electrode in contact therewith, said device being characterized by a current gain of less than unity, energizing means including a source of operating bias connected with said electrodes and operative to apply a fixed bias voltage to said base electrode wherein said device exhibits a negative resistance characteristic for predetermined values of collector voltage, and a variably tunable oscillator output circuit connected with said collector electrode and providing alternating current response in a predetermined frequency range.

7. In an oscillator circuit providing sustained oscillation without external feedback means, the combination comprising a semi-conductor device of the junction type and having a semi-conductive body, a base electrode, a collector electrode and an emitter electrode in contact therewith, means including a source of operating bias potential for applying a fixed bias to said base electrode and a variable bias to said collector electrode, said device having a negative resistance characteristic for predetermined valucs of collector voltage, and a frequency determiningcircuit connected between said emitter and collector electrodes and responsive to an alternating current of predetermined frequency therebetween.

8. A tunable oscillator comprising a semi-conductor device of the junction type having a semi-conductive body, an input electrode, an output electrode and a common electrode in contact therewith, energizing means for applying a fixed bias to said input electrode relative to said common electrode and a variable bias to said output electrode relative to said common electrode whereby said device exhibits a negative resistance characteristic, and a parallel resonant circuit connected with said output electrode.

9. In a radio receiver, a tunable source of local oscillator signals comprising a semi-conductor device having a semi-conductive body, an input electrode, an output electrode and a common electrode in contact therewith, said device having a current gain of less than unity, means ineluding a source of operating bias voltage for applying a fixed bias voltage to said input electrode for establishing a negative resistance characteristic of said device over a portion of its operating range, a frequency determining circuit connected with said common and output electrodes providing alternating current flow at a predetermined frequency therebetween, and an output circuit for said oscillator signals coupled with said frequency determining circuit.

10. An oscillator generator comprising a semi-conductor device of the junction type and having a semi-conductive body, a base electrode, a collector electrode and an emitter electrode in contact therewith, means including a source of operating bias voltage for biasing said electrodes to an operating level wherein said device exhibits a neganecting said emitter electrode with said source of reference potential, a parallel resonant circuit connected with said collector electrode, and a second source of operating voltage including variable resistance means serially connected between said parallel resonant circuit and said source of reference potential, said operating voltages being eifective for biasing said electrodes to an operating level wherein said device exhibits a negative resistance characteristic.

References Cited in the file of this patent UNITED STATES PATENTS Mallinckrodt Aug. 4, 1953 v 

